Worm Gear Definitions and Uses

A worm gear is commonly used when large gear ratios are required. Worm gears can be used for reductions as high as 300:1 or more. Worm gears are usually in line with one shaft and drive a perpendicular shaft. Worm gears are common in equipment such as milling machines, where small increment movements are needed, as little as .001 of an inch.

How a Worm Gear is Designed
A worm gear looks very much like a screw. The gear is usually designed so that a single tooth runs in a spiral along the length of the gear. The angle of this tooth is what creates the large ratios. The worm gear is usually meshed with an ordinary-looking gear.

Special Characteristics
Besides the ability to create large ratios, a result of the steep angle of the worm drive which results in a low efficiency of the gear, a worm gear set has another unique feature. While the worm gear can always drive the opposing gear, however, dependent on the angle of the worm gear, the gear may or may not drive the worm. This is very useful for certain machines like conveyors where the feature can act as a brake.

Chinabase Worm Gear

Uses for Worm Gears
Machine Heads
Worm gears are also frequently used in the tuning mechanisms (called machine heads) of popular musical instruments such as guitars, basses and mandolins. Force reduction is one reason for using worm drives with machine heads, and another is that worms tend to lock worm gears wherever they are, an important attribute for a tuned string. It should be noted that the worms on machine heads have a special cut that allows them to be moved in either direction---to tune the string up or down. Simply cut worms can be turned in only one direction.

Conveyers and Gates
Simple worm drives can be turned in only one direction, which can be a blessing. Motors that operate conveyor belts should lock up when the motor is off so that the conveyor belt never runs backward. Sometimes the automatic gates that use worm drives to open and close will have two worm dives---one to open the gate and one to close it---so that it locks in either direction and cannot be forced. Worms always lock worm gears, but sometimes, depending on how the worms are cut, they can also assure that the worm gear moves in only one direction.

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